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Dark net child sex abuse images 'epidemic'

19 June 2014 Last updated at 12:38 BST

Images of child abuse have become "an epidemic" according to one senior police officer in the United States.

He spoke after a BBC investigation found that thousands of paedophiles are operating on the so-called dark net.

The criminals use this hidden network to share indecent images of children, making them very difficult to trace.

Angus Crawford reports from Los Angeles.